1. Field of the Invention
This invention relates to a pressure foot for a machine tool such as a router.
2. Description of the Prior Art
In the operation of automatic routing machines, it is conventional to position a stack of workpieces, such as those used in producing printed circuit boards, on the worktable, holding them in place by tooling pins which extend through openings in the workpieces. For accuracy, there is a close fit between the tooling pins and the workpieces at the openings so that there is no clearance around the pins to permit relative lateral movement. It has been necessary to provide these tooling pins in the portions of the workpieces which are cut out, as well as the portions outside of the cut line, because otherwise the cutout portions will be moved laterally during the cutting operation and an accurate cut will not be produced. The lateral movement of the cutout portion will occur during the last increment of the cut, arising from the lateral force produced by the router bit as the worktable is moved relative to the spindle. Prior to that time, the portion of the workpiece to be cut out will be joined to the portion outside of the cut line by sufficient material to prevent relative movement. When the cut is nearly complete, however, the connecting portion becomes very small and lacks the strength to withstand the lateral force of the router. Thus, unless it has been held by tooling pins or other auxiliary clamping members, the cutout portion will break off or move in any event as the connecting portion is cut through, and its edge will not be accurately formed.
The necessity for using tooling pins in the cutout portions has substantially increased the production time for the machine. The drilling of the various holes for the tooling pins and the close tolerances required take a substantial amount of the operator's time in preparing the workpieces for routing and installing them on the worktable. After the routing operation is complete, additional time is expended in prying the cutout parts off of the tooling pins that hold them. Consequently, the production rate of a routing machine has been slowed and expenses have been increased because of the need for pinning the portions of the workpieces to be cut out.